Adapted from Cook's Illustrated
2 cups plus 2 tablespoons flour
1/2 teaspoon salt
1 1/2 sticks (12 tablespoons) butter, melted and cooled slightly
1 cup brown sugar
1/2 cup sugar
1 egg yolk
2 teaspoons vanilla
2 cups chocolate chunks (I chopped a 4-ounce Ghirardelli white chocolate bar, a milk chocolate bar, and a semi-sweet chocolate bar)
Preheat oven to 325º. Line a 9 x 13 pan with non-stick foil or regular foil sprayed with cooking spray.
Whisk together the melted butter and sugar. Add egg, egg yolk and vanilla and mix well. Fold in the dry ingredients with spatula or wooden spoon being careful not to over mix. Fold in chocolate chunks.
Spread dough evenly into pan. Bake 24-28 minutes, till golden brown. Cool in pan, then using foil to remove bars from pan, and cut to serve.